The present invention relates to digital printing systems, such as those using xerography, and in particular relates to a system for creating various types of test images as desired, for uses incidental to a printing process.
In digital printing, digital image relating to an image desired to be printed is retained in a computer. The data is then processed in various ways, such as by decompression, decomposition (such as from a xe2x80x9cpage description languagexe2x80x9d or other format), and/or otherwise prepared for the direct operation of printing hardware. With a xerographic xe2x80x9claser printer,xe2x80x9d one or more lasers are modulated over time according to the image data to imagewise discharge a charge receptor to create the desired image; with an ink-jet printing apparatus, the image data is ultimately used to activate ink-jet ejectors to create the desired image.
Incidental to any type of digital printing may be a need to have the printing hardware create specialized images, which will here be called xe2x80x9ctest marksxe2x80x9d but are typically called xe2x80x9ctest patchesxe2x80x9d or xe2x80x9ctest patterns,xe2x80x9d for objective evaluation. Such test patches may include patches of certain halftone values, patterns of certain configurations, such as spaced lines, chevrons, or bull""s eyes, or combinations of colors. These test patches may be made on sheets such as of a type of sheet on which regular output is made, or, particularly in xerography, made only on the charge receptor and cleaned off. The test patches are typically measured and evaluated by optical test equipment, such as an optical densitometer or colorimeter within a printer itself. In xerography such test patches on a charge receptor can be tested for electrostatic properties, such as with an electrostatic voltmeter. Measurements of actual test patches made by the test equipment or by integral sensing means within the printer can then be fed into control systems which oversee and control print quality. Typically, the test patterns or patches generated by printer control software together with automatic sensing means, and automatic control algorithms are utilized to control and adjust internal printer activators for process control functions. All these elements cooperate to form automatic closed loop process control requirements.
Another type of specialized image useful in digital printing of any type is xe2x80x9cregistrationxe2x80x9d or xe2x80x9cfiducialxe2x80x9d marks, which have the function of facilitating optical tests and measurement of image placement, particularly the registration of multiple, superimposed color separations. Such registration marks are, for purposes of the present application, xe2x80x9ctest marksxe2x80x9d as well.
In the prior art, mechanisms, particularly software mechanisms, for creation of test patches are typically dedicated to the particular hardware design of a printer. Typically, test patches can be created only of a particular type (such as predetermined halftone screens) and in certain fixed locations (such as in interdocument zones on a charge receptor), given a particular machine design; to change these parameters of test patches would typically require significant changes in the hardware and the software of the printer. Another possible technique for generation of test patches of a predetermined type would be to send to the printer image data, through the standard channel for receiving document data, including test patches of a desired type and in a desired location; however, this technique has practical disadvantages, such as consumption of memory and interruptions to the flow of data for images desired to be printed, thereby degrading performance and reliability of the printer.
The present invention relates to a versatile system for creating test patches of various types and in various locations on demand, in a manner which minimizes system image data memory use and which operates in an independent parallel data path, which is applicable to various types of printing hardware.
U.S. Pat. No. 5,450,165 describes a system in which image data associated with images desired to be printed is polled for areas which are incidentally usable as test patches.
U.S. Pat. No. 5,652,946 discloses a system for placing test patches in interdocument zones in a xerographic printer. The system uses timing values associated with different-sized images being printed to determine locations of interdocument zones.
U.S. Pat. No. 6,167,217 discloses a system which determines when test patches should be generated and tested, based on activities of the control system of the printer.
U.S. patent application Ser. No. 09/662,197, filed Sep. 14, 2000, entitled xe2x80x9cColor Printing Image Bearing Member Color Registration System,xe2x80x9d assigned to the assignee hereof, and allowed but not issued as of the filing hereof (and therefore not prior art), gives a general overview of a fiducial-mark registration system in the context of an image-on-image xerographic color printer.
According to one aspect of the present invention, there is provided a method of operating a printing apparatus, comprising the steps of entering, through a user interface associated with the printing apparatus, data relating to a desired location of a test mark within an imageable area; and causing the printing hardware to place the test mark in the imageable area.
According to another aspect of the present invention, there is provided a method of operating a printing apparatus, comprising the steps of reading, from a memory, data relating to a desired location for a test mark within an imageable area; determining a real-time opportunity for creating the test mark at the desired location within the imageable area; and causing the printing apparatus to create the test mark at the desired location when an opportunity for creating the test mark at the desired location within the imageable area is determined.
According to another aspect of the present invention, there is provided an apparatus for digital printing, comprising a memory for retaining data relating to a desired location of a test mark within an imageable area; counting means for determining a condition for printing at the desired location within the imageable area; and image generating means for causing the printing apparatus to create the test mark at the desired location.